1. Field of the Invention
This invention relates to an addition type silicone rubber composition capable of forming bubble-free molded parts and a method for preparing the same.
2. Prior Art
Silicone rubber is often used as medical parts because of heat, low-temperature and weathering resistance and because it can be molded into transparent parts and is biologically compatible. Silicone rubber of the addition type is generally used in the medical field. It is a common practice to add vulcanization retarders or control agents such as benzotriazole, acetylene alcohol derivatives and triphenyl phosphite to addition type silicone rubber compositions since curing reaction can take place at room temperature simply by mixing crosslinking agents and catalysts with the compositions.
However, when the control agents are added to addition type silicone rubber compositions such that a sufficient pot life may be available in extrusion molding the compositions and curing them by hot air vulcanization (HAV), most extrusion molded parts contain bubbles. Such bubbling is avoided by several countermeasures of increasing the amount of catalyst, reducing the amount of control agent, and increasing the plasticity of compound. These countermeasures, however, are accompanied with disadvantages of a shortened pot life, significantly disturbed extrusion, inefficient working, and poor molding appearance.